Multiple mobile communication systems have been developed in the evolution of mobile communications, for example, the second Generation (2G) mobile telecommunications system, and the third Generation (3G) mobile telecommunications system. The 2G includes: Global System for Mobile Communications (GSM), General Packet Radio System (GPRS), Enhanced Data rates for GSM Evolution (EDGE), Code Division Multiple Access (CDMA); and the 3G includes: Universal Mobile Telecommunications System (UMTS), Wideband CDMA (WCDMA), Time Division—Synchronous CDMA (TD-SCDMA), and Next Generation Network (NGN) system such as Long Term Evolution (LTE). The major difference between the mobile telecommunications systems is the radio air interface technology. Different networks match different radio air interface standards. The Radio Access Network (RAN) and the Core Network (CN) of one system are different from the RAN and the CN of another system in the network architecture and the protocol stack.
The GPRS is overlaid onto the existing GSM network, and a packet switching function entity is introduced into the GSM network to support the packet services for mobile subscribers. The structure of the GPRS transmission protocol stack is shown in FIG. 1.
The Mobile Station (MS) is a function unit that provides application interfaces and services for the user, and is responsible for the communication with another corresponding entity on the network over the radio interface. The functions and the overall protocol structure of the MS comply with standards. Messages are transmitted between the MS (such as the mobile phone and vehicle-mounted station) and the BSS through a Um interface, and the CN interface between the BBS and the Serving GPRS Support Node (SGSN) is a Gb interface. The Gb interface uses Frame Relay (FR) for lower-layer transmission, and uses the BSS GPRS protocol (BSSGP) for signaling management. The signaling transmission shares a protocol stack with data transmission below the Logical Link Control (LLC) layer. That is, the control plane (control signaling plane) of the Gb interface is not separated from the user plane (user transmission plane), and the transmission resources are shared by the control plane and the user plane. On the user plane, data is transmitted between the MS and the SGSN via a Sub-Network Dependent Convergence Protocol (SNDCP). On the control plane, a GPRS Mobility Management/Session Management (GMM/SM) protocol (which is not illustrated in the figure) is applied between the MS and the SGSN to implement mobility management and network access control.
The EDGE is an enhancement of the GPRS. The EDGE provides new modulation modes and channel coding to improve the Packet Switched (PS) service bandwidth. The change between the EDGE and the GPRS is limited to the Radio Link Control (RLC) and Media Access Control (MAC) protocol layers and physical layers of the air interface, and the GPRS network architecture remains unchanged in the EDGE. Theoretically, the maximum data rate of each MS in the GPRS is 160 Kbit/s; and when the EDGE air interface uses 8 timeslots, the maximum data rate of the EDGE is 473 Kbit/s.
The WCDMA and TD-SCDMA systems are 3G mobile telecommunications systems, and their maximum data rate is up to 2000 Kbit/s. They employ almost the same CN specifications, but employ different air interface technologies. High-Speed Packet Access (HSPA) is an improvement of the WCDMA air interface technology, and increases the data rate of the PS services. The BSS of the UMTS is a UMTS Terrestrial Radio Access Network (UTRAN), which is interfaced with the CN through an Iu interface. The PS interface is an Iu PS interface, and the protocol stack structure of the Iu PS interface of the UMTS is shown in FIG. 2.
The Iu interface is an open standard interface. The control plane protocols of the Iu PS interface include: the Radio Access Network Application Protocol (RANAP), Signaling System Number 7 (SS7), and Stream Control Transmission Protocol (SCTP); the user plane protocols of the Iu PS interface include: the GPRS Tunneling Protocol for User Plane (GTPU), and User Datagram Protocol (UDP).
The LTE system is a long term evolution project of the third Generation Partnership Project (3GPP), and its core is an all-IP, wireless broadband and flat architecture. The flat network architecture of the LTE system includes two layers. Its CN interface is an S1 interface; its protocol stack structure is shown in FIG. 3; and the S1 interface is a RANAP improvement based on the Iu interface. On the control plane, the S1 interface application protocol (S1-AP) replaces the RANAP of the Iu-PS interface; on the user plane, the enhanced GTPU (namely, GTPU′) is applied. Currently, the standards are being developed for the LTE system.
Mobile telecommunications networks need to evolve toward the NGN to support new service requirements and cater for the fast development of data services. According to the relation between 3GPP standards, the network may evolve along different paths: evolution from 2G to 3G and NGN, for example, GPRS (EDGE)→WCDMA (HSPA)→LTE; or evolution from 2G to NGN directly, for example, GPRS (EDGE)→LTE; or evolution in the same generation with some improvements in technology and performance, for example, GPRS→EDGE, and GPRS (EDGE)→GSM EDGE RAN (GERAN).
The existing GPRS (EDGE) network evolution involves the following defects:
The control plane is not separated from the user plane of the Gb interface of the GPRS network, and the resources are shareable to all users. The Gb interface of the GPRS network is sharply different from the 3G CN interface where the control plane is separated from the user plane, and the network evolution is difficult.
After the air interface technology is improved for the GPRS (EDGE) network, the Gb interface bandwidth and the delay constitute a bottleneck. The Gb interface handover is of low quality and can hardly meet the development of the packet data services. Because the Gb interface protocol stack is sharply different from the CN interface protocol stack for the 3G and the NGN, better CN interfaces such as Iu PS and S1 are not directly applicable.
The network upgrade according to network standards is a process of replacing equipment, and the equipment is generally not backward compatible, and the MS of the GPRS (EDGE) network is not applicable in the new network. For example, a GPRS (EDGE) mobile phone is unable to access the CN using the Iu PS interface, which restricts the network evolution.
In practice, network upgrade needs to allow for backward compatibility and smooth evolution to save costs. The order of priority in upgrade is: MS, base station, and then CN. If the operator has plenty of existing networks and the upgrade solution does not ensure backward compatibility with the MS or network, the network upgrade cost is too high. In this case, the existing investments are wasted, and the waste of investments is enormous.
Likewise, the 3G network also needs to evolve toward the unified LTE CN. However, different network systems have different CNs. Therefore, the CN cannot be solely improved during network evolution. The inconsistent CN interfaces make it difficult to perform network interworking and unified management, and hinder the smooth evolution of the network.
As shown in FIG. 4, the 3GPP proposes to use the GERAN Rel′5 as the evolved version of the GSM/EDGE, namely, GPRS (EDGE) evolving to GERAN, which is evolution in the same generation and enables the connection from the 2G network to the 3G CN.
However, as shown in FIG. 1 and FIG. 4, compared with the GPRS (EDGE), the GERAN changes the radio protocol massively and increases the complexity of the air interface protocol; the change of the GERAN radio interface imposes a great impact on the BSS and the MS, and makes it necessary to change the BSS and the MS accordingly. The existing GPRS (EDGE) MS is not applicable in a GERAN network. Therefore, the evolution from the GPRS (EDGE) to the GERAN also lacks smoothness and backward compatibility, and involves a huge waste of the existing investments.